The present application claims priority to Japanese Application(s) No(s). P2001-092252 filed Mar. 28, 2001, which application(s) is/are incorporated herein by reference to the extent permitted by law.
The present invention relates to a method of fabricating a semiconductor device, and particularly to a method of fabricating a semiconductor device, in which an anti-reflection film is etched with a resist taken as a mask.
In recent years, as exemplified by VLSI (Very Large Scale Integration), semiconductor devices have become finer along with a trend toward a higher degree of integration and higher function thereof. As a result, to make a line width of such a semiconductor device fine, it is required to shorten a wavelength of exposure light used for photolithography, which wavelength determines a minimum line width, and therefore, it becomes difficult to control a dimension of the line width.
A related art method of forming a resist pattern has been carried out by forming a resist film on an under substrate, selectively exposing the resist film to light having a single wavelength, such as a g-ray (wavelength: 436 nm), an i-ray (wavelength: 365 nm), or a KrF excimer laser beam (wavelength: 248 nm), and developing the resist film with an alkali containing water solution. By the way, in the case of performing exposure using light having such a single wavelength, a shape of the resist may be often degraded due to light reflected from the under substrate. Such reflection of light from the under substrate is called xe2x80x9chalationxe2x80x9d. On the other hand, at the time of patterning of the resist, a standing wave is generated by multi-interference of light in the resist film upon exposure, and in this case, if a thickness of the resist film is uneven depending on a difference-in-height of the under substrate, a quantity of incident light reaching an interface between the resist film and the under substrate and a quantity of reflected light from the interface between the resist film and the under substrate are varied depending on the uneven thickness of the resist film, with a result that a difference in quantity of light absorbed in the resist occurs between a thick portion and a thin portion of the resist film, to thereby vary a pattern dimension of the resist. In other words, an uneven thickness of the resist emerges as an uneven pattern dimension of the resist by the effect of the standing wave, so that it is difficult to accurately control the pattern dimension of the resist.
In fabrication of a semiconductor device, a variation in pattern dimension of a resist by halation and the standing wave effect causes problems associated with a variation in transistor characteristics, disconnection, short-circuit, and the like. In particular, a quantity of light absorbed in the resist, which is dependent on the standing wave effect, is finely changed depending on a light absorptivity of the resist film, a kind of an under substrate, and a difference-in-height of a surface of the under substrate, with a result that it is difficult to control a pattern dimension of the resist obtained after exposure and development. Such a problem commonly occurs for any kind of resist, and becomes more significant as a pattern dimension of a resist becomes finer.
To suppress such a standing wave effect, there has been proposed a method of providing an organic based anti-reflection film under a resist. The anti-reflection film contains a pigment capable of absorbing light having a wavelength used for exposure. Reflection of light from an under substrate can be perfectly shielded by optimizing a thickness of the anti-reflection film.
The formation of the anti-reflection film, however, has a problem. Since a composition of the anti-reflection film is closer to that of a resist, if an etching gas containing oxygen is used in a dry etching step for etching the anti-reflection film, the resist film may be etched at the time of etching the anti-reflection film, so that an opening portion of the resist becomes wider than that at the time of patterning by etching.
Another problem caused by formation of an anti-reflection film is as follows. If an under substrate has a difference-in-height, a thickness of the antireflection film formed thereon is varied depending on the difference-in-height of the under substrate, like the above-described variation in thickness of a resist. To be more specific, the anti-reflection film is thin at its portion positioned at an upper portion of the difference-in-height of the under substrate and is thin at its portion positioned at a lower portion of the difference-in-height of the under substrate. The variation in thickness of the anti-reflection film, generated at this stage, is dependent on a viscosity of a material of the anti-reflection film, and it becomes smaller when the viscosity of the material of the anti-reflection film becomes higher. The variation in thickness of the anti-reflection film, however, cannot be perfectly eliminated even by adjusting the viscosity of the material of the anti-reflection film. Accordingly, etching of the anti-reflection film must be performed under an etching condition optimized for a thick portion of the anti-reflection film. In this case, however, etching of a thin portion of the anti-reflection film becomes excessive, and thereby an opening portion of the resist is etched along with the etching of the anti-reflection film, to be extended in the lateral direction, thereby increasing a variation in pattern dimension of the resist.
A further problem caused by formation of an antireflection film is as follows. In the case where a thickness of an anti-reflection film is uneven, a variation in pattern dimension occurs in the antireflection film by the standing wave effect due to interference of incident light with reflected light. Such a dimensional variation is negligible if a thickness of the anti-reflection film is sufficiently large (0.2 xcexcm or more); however, in this case, it is required to prolong an etching time for etching the anti-reflection film. Consequently, as described above, since a composition of the anti-reflection film is closer to that of a resist, etching of the anti-reflection film is accompanied by etching of the resist film, to extend an opening portion of the resist, thereby causing a variation in pattern dimension.
An additional problem caused by formation of an anti-reflection film is that an insulating film such as a silicon oxide film, formed under the anti-reflection film, must be etched by an etching system different from that used for etching the anti-reflection film after etching of the anti-reflection film, with a result that the number of etching steps is increased.
An object of the present invention is to provide a method of fabricating a semiconductor device, which is capable of etching an anti-reflection film with a resist taken as a mask while suppressing a variation in a dimension of a pattern.
Another object of the present invention is to provide a method of fabricating a semiconductor device, which is capable of continuously etching an anti-reflection film and an insulating film.
To achieve the above object, according to an aspect of the present invention, there is provided a method of fabricating a semiconductor device, in which an anti-reflection film is etched with a resist taken as mask, including the steps of: forming an insulating film on a wafer substrate and forming an anti-reflection film on the insulating film; forming a resist on the anti-reflection film and forming an opening portion in the resist; and removing a portion, positioned at the opening portion of said resist, of the anti-reflection film by etching using an etching gas containing a substituted hydrocarbon with a halogen.
With this configuration, at the time of etching the anti-reflection film, the substituted hydrocarbon with a halogen contained in the etching gas is formed as a carbonaceous deposit on side walls of an opening portion formed in the resist and side walls of an opening portion, formed by etching, of the anti-reflection film. The deposit acts as a side wall blocking film, which can suppress, even if a thickness of each of the resist and the anti-reflection film is uneven, lateral extension of the opening portion of the resist and the opening portion of the anti-reflection film. As a result, it is possible to perform anisotropic etching of the anti-reflection film, and hence to fabricate a semiconductor device with an accurately formed pattern.
Also, according to the present invention, etching characteristics such as an etching rate of the anti-reflection film, and an etching selection ratio of the anti-reflection film to the resist, and an etching selection ratio of an SiO2 film to a polysilicon film can be controlled by changing a composition ratio of the substituted hydrocarbon with a halogen contained in the etching gas and a composition ratio of oxygen contained in the etching gas.
Further, according to the present invention, the underlying SiO2 film can be continuously etched after etching of the anti-reflection film by optimizing the composition ratio of oxygen contained in the etching gas containing the substituted hydrocarbon with a halogen. As a result, it is possible to continuously etch the anti-reflection film and the SiO2 film by the same etching system and hence to reduce the number of steps and improve the fabrication efficiency.